Method of forming semiconductor device having a conductive via structure

ABSTRACT

A method for fabricating a semiconductor device includes forming a first photo-sensitive layer over a contact pad, wherein the contact pad is on a substrate. The method further includes patterning the first photo-sensitive layer to form a first opening over a portion of the contact pad. The method further includes plating a conductive via in the first opening; and removing the first photo-sensitive layer. The method further includes forming a passivation layer over the substrate, contact pad, and conductive via, and exposing the conductive via by grinding the passivation layer. The method further includes forming a second photo-sensitive layer over the conductive via and passivation layer. The method further includes patterning the second photo-sensitive layer to form a second opening larger than and completely exposing the conductive via. The method further includes plating a conductive pillar in the second opening; and removing the second photo-sensitive layer.

PRIORITY CLAIM

The present application is a divisional of U.S. application Ser. No. 13/116,201, filed May 26, 2011, which is incorporated herein by reference in its entirety.

FIELD OF THE INVENTION

The invention relates to integrated circuit fabrication and, more particularly, to a semiconductor device with a conductive via.

BACKGROUND

Modern integrated circuits (ICs) are made up of literally millions of active devices, such as diodes and transistors, and passive devices, such as inductors, capacitors and resistors. These devices are initially isolated from each other, but are later interconnected together to form functional circuits. Typical interconnect structures include lateral interconnections, such as metal lines (wirings), and vertical interconnections, such as vias and contacts. Interconnections are increasingly determining the limits of performance and the density of modern ICs. On top of the interconnect structures, contact pads are formed on the interconnect structures and exposed on top surface of the respective chip for IC package. Electrical connections are made through contact pads to connect the chip to a package substrate or another die. Contact pads can be used for wire bonding or flip-chip bonding during IC packaging.

Flip-chip bonding utilizes bumps to establish electrical contact between a chip's contact pads and the package substrate. Structurally, a bump actually contains the bump itself and a so-called under bump metallurgy (UBM) layer located between the bump and a contact pad. An UBM layer generally comprises a diffusion barrier layer (or a glue layer) and a seed layer, arranged in that order, on the contact pad. The bumps themselves, based on the material used, are classified as solder bumps, gold bumps, copper pillar bumps and bumps with mixed metals. Recently, copper pillar bump technology has been proposed. Instead of using a solder bump, the electronic component is connected to a substrate by a copper pillar bump, which achieves finer pitch with minimum probability of bump bridging, reduces the capacitance load for the circuits, and allows the electronic component to perform at higher frequencies.

However, there are challenges to implementing such features and processes in IC fabrication. For example, delamination between an inter-metal dielectric (IMD) layer and an interconnect structure overlying the integrated circuits due to high stress from a copper pillar. Accordingly, what is needed is an improved bump structure and method of bump formation.

BRIEF DESCRIPTION OF THE DRAWINGS

The present disclosure is best understood from the following detailed description when read with the accompanying figures. It is emphasized that, in accordance with the standard practice in the industry, various features are not drawn to scale and are used for illustration purposes only. In fact, the dimensions of the various features may be arbitrarily increased or reduced for clarity of discussion.

FIG. 1 is a flowchart illustrating a method for fabricating a semiconductor device comprising a conductive via according to various aspects of the present disclosure;

FIGS. 2-9B show schematic cross-sectional views of a conductive via of a semiconductor device at various stages of fabrication according to various aspects of the present disclosure; and

FIG. 10 shows schematic top-down views of a conductive via of a semiconductor device according to various aspects of the present disclosure.

DESCRIPTION

It is understood that the following disclosure provides many different embodiments, or examples, for implementing different features of the invention. Specific examples of components and arrangements are described below to simplify the present disclosure. These are, of course, merely examples and are not intended to be limiting. For example, the formation of a first feature over or on a second feature in the description that follows may include embodiments in which the first and second features are formed in direct contact, and may also include embodiments in which additional features may be formed between the first and second features, such that the first and second features may not be in direct contact. Various features may be arbitrarily drawn in different scales for simplicity and clarity.

FIG. 1 is a flowchart illustrating a method 100 for fabricating a semiconductor device 200 comprising a conductive via 304 a or 304 b (shown in FIGS. 4A through 9B) according to various aspects of the present disclosure. FIGS. 2-9B show schematic cross-sectional views of a conductive via 304 a or 304 b of a semiconductor device 200 at various stages of fabrication according to various aspects of the present disclosure. It is understood that additional processes may be provided before, during, and after the method 100 of FIG. 1, and that some other processes may only be briefly described herein. Also, FIGS. 1 through 9B are simplified for a better understanding of the inventive concepts of the present disclosure. For example, although the figures illustrate the conductive via 304 a or 304 b of a semiconductor device 200, it is understood the semiconductor device 200 may be part of an integrated circuit (IC) package that further comprises a number of other components such as under-fill, lead-frame, etc.

Referring to FIGS. 1 and 2, the method 100 begins at step 102 wherein a substrate 202 having a contact pad 204 is provided. The substrate 202 may comprise a silicon substrate. The substrate 202 may alternatively comprise silicon germanium, gallium arsenic, or other suitable semiconductor materials. The substrate 202 may further comprise other features such as various doped regions, a buried layer, and/or an epitaxy layer. Furthermore, the substrate 202 may be a semiconductor on insulator such as silicon on insulator (SOI) or silicon on sapphire. In other embodiments, the substrate 202 may comprise a doped epi layer, a gradient semiconductor layer, and/or may further include a semiconductor layer overlying another semiconductor layer of a different type such as a silicon layer on a silicon germanium layer. In other examples, a compound semiconductor substrate 202 may comprise a multilayer silicon structure or a silicon substrate may include a multilayer compound semiconductor structure.

The substrate 202 further comprises a plurality of isolation regions (not shown). The isolation regions may utilize isolation technology, such as local oxidation of silicon (LOCOS) or shallow trench isolation (STI), to define and electrically isolate the various microelectronic elements (not shown). In the present embodiment, the isolation regions include a STI. The isolation regions may comprise silicon oxide, silicon nitride, silicon oxynitride, fluoride-doped silicate glass (FSG), a low-K dielectric material, other suitable materials, and/or combinations thereof. The isolation regions, and in the present embodiment, the STI, may be formed by any suitable process. As one example, the formation of the STI may include patterning the semiconductor substrate 202 by a conventional photolithography process, etching a trench in the substrate 202 (for example, by using a dry etching, wet etching, and/or plasma etching process), and filling the trench (for example, by using a chemical vapor deposition process) with a dielectric material. In some embodiments, the filled trench may have a multi-layer structure such as a thermal oxide liner layer filled with silicon nitride or silicon oxide.

Examples of the various microelectronic elements that may be formed in the substrate 202 include transistors (e.g., p-channel/n-channel metal oxide semiconductor field effect transistors (pMOSFETs/nMOSFETs), bipolar junction transistors (BJTs), high voltage transistors, high frequency transistors, etc.); diodes; resistors; capacitors; inductors; fuses; and other suitable elements. Various processes are performed to form the various microelectronic elements including deposition, photolithography, implantation, etching, annealing, and other suitable processes. The microelectronic elements are interconnected to form the IC device, such as a logic device, memory device (e.g., static random access memory or SRAM), radio frequency (RF) device, input/output (I/O) device, system-on-chip (SoC) device, combinations thereof, and other suitable types of devices.

The substrate 202 further comprises inter-layer dielectric (ILD) layers, inter-metal dielectric (IMD) layers and an interconnect structure overlying the integrated circuits. The IMD layers in the interconnect structure include low-k dielectric materials, un-doped silicate glass (USG), fluorine-doped silicate glass (FSG), carbon-doped silicate glass, silicon nitride, silicon oxynitride, or other commonly used materials. The dielectric constants (k value) of the low-k dielectric materials may be less than about 3.9, or less than about 2.3. Metal lines in the interconnect structure may be formed of copper or copper alloys. One skilled in the art will realize the formation details of the interconnect structure.

A contact pad 204 is a top interconnect layer formed in a top-level IMD layer 206, which is a portion of conductive routes and has an exposed surface treated by a planarization process, such as chemical mechanical polishing (CMP), if necessary. Suitable materials for the contact pad 204 may comprise, but are not limited to, for example copper (Cu), aluminum (Al), AlCu, aluminum alloy, copper alloy, or other conductive materials. The contact pad 204 is used in the bonding process to connect the integrated circuits in the respective chip to external features.

It should be noted that a large volume of a conductive pillar over the contact pad 204 provides higher mechanical strength and lower resistance for flip-chip bonding, but may transmit high stress to an interface of the IMD layers and interconnect structure, resulting in delamination between the IMD layers and interconnect structure.

Accordingly, the processing discussed below with reference to FIGS. 3A-9B may use a small-volume conductive via between the contact pad 204 and a conductive pillar to provide enough mechanical strength and lower resistance for flip-chip bonding, but transmit low stress to an interface of the IMD layers and interconnect structure, problems associated with high stress from a large-volume conductive pillar between the IMD layers and interconnect structure may be avoided. This can reduce delamination between the IMD layers and interconnect structure and upgrade device performance.

Referring to FIGS. 3A and 3B, a first conductive layer 208 a or 208 b is formed over the contact pad 204 and IMD layer 206. FIGS. 3A and 3B show different embodiments of the first conductive layer (208 a in FIG. 3A and 208 b in FIG. 3B). Any standard seed material may be employed in embodiments of the disclosure. In one embodiment, the first conductive layer 208 a or 208 b is formed of copper by physical vapor deposition (PVD) or sputtering. In another embodiment, the first conductive layer 208 a or 208 b may be formed of copper alloys that comprise silver, chromium, nickel, tin, gold, and combinations thereof. The first conductive layer 208 a or 208 b is deposited to a thickness t₁ of between about 0.4 and 0.6 μm.

The method 100 in FIG. 1 continues with step 104 in which a first photo-sensitive layer 302 a or 302 b is formed over the first conductive layer 208 a or 208 b. In some embodiments, the photo-sensitive layer 302 a or 302 b may be a dry film or a photo-resist film. The photo-sensitive layer 302 a or 302 b may be applied over the first conductive layer 208 a or 208 b by conventional deposition processes. In one embodiment, the photo-sensitive layer 302 a or 302 b is formed by laminating a dry film over the first conductive layer 208 a or 208 b having a thickness of from about 20 μm to about 30 μm. In another embodiment, the photo-sensitive layer 302 a or 302 b is formed by spin-coating a photo-resist film over the first conductive layer 208 a or 208 b to obtain a thickness of from about 20 μm to about 30 μm. It is understood that the thickness of the photo-sensitive layer 302 a or 302 b can be controlled and selected to be a desirable value, this especially in relation to the thickness of the column of a to-be-formed conductive via material.

The method 100 in FIG. 1 continues with step 106 in which the structures in FIGS. 3A and 3B are produced by patterning the first photo-sensitive layer 302 a or 302 b to form a first opening 402 a or 402 b over a portion of the contact pad 204. FIGS. 3A and 3B show different embodiments of the first opening (402 a in FIG. 3A and 402 b in FIG. 3B). In some vertical embodiments, the first opening 402 a comprises vertical sidewalls where the first photo-sensitive layer 302 a meets the first conductive layer 208 a (shown in FIG. 3A). In some tapered embodiments, a tapered structure is formed by under-exposing or under-developing the first photo-sensitive layer 302 b, thereby the first opening 402 b comprises tapers inward so that there is an acute contact angle where the first photo-sensitive layer 302 b meets the first conductive layer 208 b (shown in FIG. 3B). In the present embodiment, the first photo-sensitive layer 302 a or 302 b is patterned by conventional processes to form the first opening 402 a or 402 b over a portion of the contact pad 204, exposing a portion of the first conductive layer 208 a or 208 b for defining a window of a conductive via 304 a (shown in FIGS. 4A through 9A) or 304 b (shown in FIGS. 4B through 9B). In one embodiment, the first opening 402 a or 402 b has a first width W₁ in the range of about 40 to 45 μm. In some embodiments, the patterned first photo-sensitive layer 302 a or 302 b has an additional opening over the contact pad 204.

The method 100 in FIG. 1 continues with step 108 in which the structure in FIGS. 4A and 4B are produced by plating a conductive via 304 a or 304 b in the first opening 402 a or 402 b. FIGS. 4A and 4B show different embodiments of the conductive via (304 a in FIG. 4A and 304 b in FIG. 4B). In the present embodiment, the first opening 402 a or 402 b is partially or fully filled with a conductive via 304 a or 304 b by suitable formation methods. In the present embodiment, the conductive via 304 a or 304 b is formed upward along the first opening 402 a or 402 b using the first conductive layer 208 a or 208 b as a seed layer.

The conductive via 304 a or 304 b comprises a copper via, also referred to as a copper via 304 a or 304 b. The copper via 304 a or 304 b is intended to comprise substantially a layer including pure elemental copper, copper containing unavoidable impurities, and copper alloys containing minor amounts of elements such as tantalum, indium, tin, zinc, manganese, chromium, titanium, germanium, strontium, platinum, magnesium, aluminum or zirconium. In some embodiments, the conductive via 304 a or 304 b and the first conductive layer 208 a or 208 b may be formed from the same material. The formation methods may include sputtering, printing, electro plating, electroless plating, and commonly used chemical vapor deposition (CVD) methods. For example, electro-chemical plating (ECP) is carried out to form the copper via 304 a or 304 b. In an exemplary embodiment, the thickness t₂ of the conductive via 304 a or 304 b is greater than 20 μm. For example, the conductive via 304 a or 304 b is of about 20-30 μm thickness, although the thickness may be greater or smaller.

The method 100 in FIG. 1 continues with step 110 in which the structure in FIGS. 5A and 5B is produced by removing the first photo-sensitive layer 302 a or 302 b. FIGS. 5A and 5B show different embodiments of the conductive via (304 a in FIG. 5A and 304 b in FIG. 5B). In the present embodiment, the first photo-sensitive layer 302 a or 302 b may be removed using conventional wet etching or dry etching processes.

Then, using the conductive via 304 a or 304 b as a hard-mask, FIGS. 5A and 5B also show the substrate 202 of FIGS. 4A and 4B after a portion of the first conductive layer 208 a or 208 b is removed to expose the IMD layer 206 and a portion of the contact pad 204. The step of removing a portion of the first conductive layer 208 a or 208 b is performed using a wet etching process. For example, the wet etching process comprises removing a portion of the first conductive layer 208 a or 208 b in a solution comprising H₃PO₃ and H₂O₂.

In the vertical embodiment, the first conductive layer 208 a may be removed until outer edges of the remaining first conductive layer 208 a are substantially aligned with outer edges of the conductive via 304 a (shown in FIG. 5A). Structurally, the conductive via 304 a actually contains the conductive via 304 a itself and remaining first conductive layer 208 a located between the conductive via 304 a and contact pad 204. Further, the conductive via 304 a comprises substantially vertical sidewalls.

In the tapered embodiment, the first conductive layer 208 b may be removed until outer edge of the remaining first conductive layer 208 b is substantially aligned with the outer edge of a bottom portion of the conductive via 304 b (shown in FIG. 5B). Structurally, the conductive via 304 b actually contains the conductive via 304 b itself and remaining first conductive layer 208 b located between the conductive via 304 b and contact pad 204. Further, the conductive via 304 b is narrower at a point 304 p of a contact with the contact pad 204.

It should be noted that additional etching increases contact resistance, resulting from the reduced contact area between the remaining first conductive layer 208 a and conductive via 304 a in the vertical embodiment, or between the remaining first conductive layer 208 b and conductive via 304 b in the tapered embodiment.

The method 100 in FIG. 1 continues with step 112 in which the structure in FIGS. 6A and 6B is produced by forming a passivation layer 306 a or 306 b over the substrate 202, contact pad 204, and conductive via 304 a or 304 b, and exposing the conductive via 304 a or 304 b by grinding the passivation layer 306 a or 306 b for allowing subsequent conductive pillar bump processes. FIGS. 6A and 6B show different embodiments of the conductive via (304 a in FIG. 6A and 304 b in FIG. 6B). In the present embodiment, the passivation layer 306 a or 306 b extends over the substrate 202 and has an opening 306 c or 306 d with a first width W₁ (i.e., almost same as the first width W₁ of the first opening 402 a or 402 b) over the contact pad 204. Thus, the conductive via 304 a or 304 b is within the opening of the passivation layer 306 a or 306 b. In some embodiments, the passivation layer 306 a or 306 b has an additional opening over the contact pad 204 and an additional conductive via within the additional opening.

In some embodiments, the passivation layer 306 is formed of a non-organic material selected from un-doped silicate glass (USG), silicon nitride, silicon oxynitride, silicon oxide, and combinations thereof. Alternatively, the passivation layer is formed of a polymer layer, such as an epoxy, polyimide, benzocyclobutene (BCB), polybenzoxazole (PBO), and the like, although other relatively soft, often organic, dielectric materials can also be used. In one embodiment, the passivation layer 306 may be formed using a chemical vapor deposition (CVD), high density plasma CVD (HDP CVD), sub-atmospheric CVD (SACVD), physical vapor deposition (PVD), or spin-on process.

Referring to FIGS. 7A and 7B, a second conductive layer 308 a or 308 b is formed over the conductive via 304 a or 304 b and passivation layer 306 a or 306 b. FIGS. 7A and 7B show different embodiments of the conductive via (304 a in FIG. 7A and 304 b in FIG. 7B). Any standard seed material may be employed in embodiments of the invention. In one embodiment, the second conductive layer 308 a or 308 b is formed of copper by physical vapor deposition (PVD) or sputtering. In another embodiment, the second conductive layer 308 a or 308 b may be formed of copper alloys that comprise silver, chromium, nickel, tin, gold, and combinations thereof. The second conductive layer 308 a or 308 b is deposited to a thickness t₃ of between about 0.4 and 0.6 μm.

The method 100 in FIG. 1 continues with step 114 in which a second photo-sensitive layer 502 a or 502 b is formed over the second conductive layer 308 a or 308 b, thereby formed over the conductive via 304 a or 304 b and passivation layer 306 a or 306 b. The second photo-sensitive layer 502 a or 502 b may be a dry film or a photo-resist film. The second photo-sensitive layer 502 a or 502 b may be applied over the second conductive layer 308 a or 308 b by conventional deposition processes. In one embodiment, the second photo-sensitive layer 502 a or 502 b is formed by laminating a dry film over the second conductive layer 308 a or 308 b having a thickness of from about 55 μm to about 60 μm. In another embodiment, the second photo-sensitive layer 502 a or 502 b is formed by spin-coating a photo-resist film over the second conductive layer 308 a or 308 b to obtain a thickness of from about 55 μm to about 60 μm. It is understood that the thickness of the second photo-sensitive layer 502 a or 502 b can be controlled and selected to be a desirable value, this especially in relation to the thickness of the column of a to-be-formed conductive pillar bump material.

For defining a window of a conductive pillar 504 a or 504 b (shown in FIGS. 8A through 9B), the method 100 in FIG. 1 continues with step 114 in which the structures in FIGS. 7A and 7B are produced by patterning the second photo-sensitive layer 502 a or 502 b to form a second opening 404 a or 404 b larger than and completely exposing the conductive via 304 a or 304 b. FIGS. 7A and 7B show different embodiments of the conductive via (304 a in FIG. 7A and 304 b in FIG. 7B). In one embodiment, the second opening 404 a or 404 b has a second width W₂ in the range of about 80 to 90 μm.

The method 100 in FIG. 1 continues with step 118 in which the structure in FIGS. 8A and 8B is produced by plating a conductive pillar 504 a or 504 b in the second opening 404 a or 404 b. FIGS. 8A and 8B show different embodiments of the conductive via (304 a in FIG. 8A and 304 b in FIG. 8B). In the present embodiment, the second opening 404 a or 404 b is partially or fully filled with the conductive pillar 504 a or 504 b by suitable formation methods. In the present embodiment, the conductive pillar 504 a or 504 b is formed upward along the second opening 404 a or 404 b using the second conductive layer 308 a or 308 b as a seed layer.

The conductive pillar 504 a or 504 b comprises a copper pillar, also referred to as a copper pillar 504 a or 504 b. The copper pillar 504 a or 504 b is intended to comprise substantially a layer including pure elemental copper, copper containing unavoidable impurities, and copper alloys containing minor amounts of elements such as tantalum, indium, tin, zinc, manganese, chromium, titanium, germanium, strontium, platinum, magnesium, aluminum or zirconium. The conductive pillar 504 a or 504 b and the second conductive layer 308 a or 308 b may be formed from the same material. The formation methods may include sputtering, printing, electro plating, electroless plating, and commonly used chemical vapor deposition (CVD) methods. For example, electro-chemical plating (ECP) is carried out to form the copper pillar 504 a or 504 b. In an exemplary embodiment, the thickness t₄ of the conductive pillar 504 a or 504 b is greater than 55 μm. For example, the conductive pillar 504 a or 504 b is about 55-60 μm thick, although the thickness may be greater or smaller.

The method 100 in FIG. 1 continues with step 120 in which the structure in FIGS. 9A and 9B is produced by removing the second photo-sensitive layer 502 a or 502 b. FIGS. 9A and 9B show different embodiments of the conductive via (304 a in FIG. 9A and 304 b in FIG. 9B). In the present embodiment, the second photo-sensitive layer 502 a or 502 b may be removed using conventional wet etching or dry etching processes.

Then, using the conductive pillar 504 a or 504 b as a hard-mask, FIGS. 9A and 9B also show the substrate 202 of FIGS. 8A and 8B after a portion of the second conductive layer 308 a or 308 b is removed to expose the passivation layer 306 a or 306 b. The step of removing a portion of the second conductive layer 308 a or 308 b is performed using a wet etching process. For example, the wet etching process comprises removing a portion of the second conductive layer 308 a or 308 b in a solution comprising H₃PO₃ and H₂O₂.

In the present embodiment, the second conductive layer 308 a or 308 b may be removed until outer edges of the remaining second conductive layer 308 a or 308 b is substantially aligned with outer edges of the conductive pillar 504 a or 504 b. It should be noted that additional etching increases contact resistance, resulting from the reduced contact area between the remaining second conductive layer 308 a and conductive pillar 504 a, or between the remaining second conductive layer 308 b and conductive pillar 504 b. Structurally, the conductive pillar 504 a actually contains the conductive pillar 504 a itself and remaining second conductive layer 308 a located between the conductive pillar 504 a and conductive via 304 a. Structurally, the conductive pillar 504 b actually contains the conductive pillar 504 b itself and remaining second conductive layer 308 b located between the conductive pillar 504 b and conductive via 304 b.

In the present embodiment, the conductive pillar 504 a or 504 b has a second width W₂ (i.e., almost same as the second width W₂ of the second opening 404 a or 404 b) completely covering the conductive via 304 a or 304 b, wherein a ratio of the first width W₁ of conductive via 304 a or 304 b to the second width W₂ of the conductive pillar 504 a or 504 b is from about 0.15 to 0.55, or a ratio of the first width W₁ of the opening 306 c or 306 d of the conductive via 304 a or 304 b to the second width W₂ of the conductive pillar 504 a or 504 b is from about 0.15 to 0.55. In some embodiments, a ratio of the thickness t₂ of the conductive via 304 a or 304 b to the thickness t₄ of the conductive pillar 505 a or 505 b is from about 0.33 to 0.55. In at least one embodiment, the conductive via 304 a or 304 b and the conductive pillar 505 a or 505 b are formed from the same material. In at least one embodiment, the conductive via 304 a or 304 b and the conductive pillar 505 a or 505 b are formed from different materials.

FIG. 10 shows schematic top-down views of the conductive via 304 a or 304 b of the semiconductor device 200 according to various aspects of the present disclosure. The top-down view of the conductive via 304 a or 304 b comprises a shape selected from circle 304 c, square 304 d, and cross 304 e.

Therefore, a semiconductor device 200 comprises a substrate 202; a contact pad 204 over the substrate 202; a passivation layer 306 a or 306 b extending over the substrate 202 and having an opening 306 c or 306 d with a first width W₁ over the contact pad 204; a conductive via 304 a or 304 b within the opening 306 c or 306 d; and a conductive pillar 504 a or 504 b having a second width W₂ completely covering the conductive via 304 a or 304 b, wherein a ratio of the first width W₁ to the second width W₂ is from about 0.15 to 0.55. The passivation layer 306 a or 306 b may have an additional opening over the contact pad 204 and an additional conductive via within the additional opening. Therefore, Applicant's method can reduce delamination between the IMD layers and interconnect structure and upgrade device performance.

Then, subsequent processes, including flip-chip processing, are performed after forming the semiconductor device 200 to complete the IC fabrication.

One aspect of this description relates to a method of fabricating a semiconductor device. The method includes forming a first photo-sensitive layer over a contact pad, wherein the contact pad is on a substrate. The method further includes patterning the first photo-sensitive layer to form a first opening over a portion of the contact pad. The method further includes plating a conductive via in the first opening; and removing the first photo-sensitive layer. The method further includes forming a passivation layer over the substrate, contact pad, and conductive via, and exposing the conductive via by grinding the passivation layer. The method further includes forming a second photo-sensitive layer over the conductive via and passivation layer. The method further includes patterning the second photo-sensitive layer to form a second opening larger than and completely exposing the conductive via. The method further includes plating a conductive pillar in the second opening; and removing the second photo-sensitive layer.

Another aspect of this description relates to a method of fabricating a semiconductor device. The method includes forming a first conductive layer over a contact pad, wherein the contact pad is on a substrate. The method further includes plating a conductive via on the first conductive layer; and forming a passivation layer over the contact pad, wherein a top surface of the conductive via is exposed by the passivation layer. The method further includes forming a second conductive layer over the conductive via and the passivation layer, wherein the second conductive layer is electrically connected to the conductive via. The method further includes plating a conductive pillar over the second conductive layer, wherein a width of the conductive pillar is greater than a width of the conductive via.

Still another aspect of this description relates to a method of fabricating a semiconductor device. The method includes forming a first conductive layer over a contact pad, wherein the contact pad is on a substrate. The method further includes plating a conductive via on the first conductive layer; and etching the first conductive layer to remove portions of the first conductive layer exposed by the conductive via. The method further includes forming a second conductive layer over the conductive via, wherein the second conductive layer is electrically connected to the conductive via. The method further includes plating a conductive pillar over the second conductive layer, wherein a width of the conductive pillar is greater than a width of the conductive via. The method further includes etching the second conductive layer to remove portions of the second conductive layer exposed by the conductive pillar.

While this disclosure has described the preferred embodiments, it is to be understood that the disclosure is not limited to the disclosed embodiments. To the contrary, it is intended to cover various modifications and similar arrangements (as would be apparent to those skilled in the art). Therefore, the scope of the appended claims should be accorded the broadest interpretation so as to encompass all such modifications and similar arrangements. 

What is claimed is:
 1. A method of fabricating a semiconductor device, comprising the steps of: forming a first photo-sensitive layer over a contact pad, wherein the contact pad is on a substrate; patterning the first photo-sensitive layer to form a first opening over a portion of the contact pad; plating a conductive via in the first opening; removing the first photo-sensitive layer; forming a passivation layer over the substrate, contact pad, and conductive via, and exposing the conductive via by grinding the passivation layer; forming a second photo-sensitive layer over the conductive via and passivation layer; patterning the second photo-sensitive layer to form a second opening larger than and completely exposing the conductive via; plating a conductive pillar in the second opening; and removing the second photo-sensitive layer.
 2. The method of claim 1, wherein the passivation layer comprises an inorganic material or a polymer layer.
 3. The method of claim 1, wherein the conductive via comprises copper or copper alloy.
 4. The method of claim 1, wherein the conductive via is narrower at a point of a contact with the contact pad than at a point of contact with the conductive pillar.
 5. The method of claim 1, wherein the conductive via comprises vertical sidewalls.
 6. The method of claim 1, wherein a top-down view of the conductive via comprises a shape selected from at least one of a circle, a square, or a cross.
 7. The method of claim 1, wherein the conductive pillar comprises copper or copper alloy.
 8. The method of claim 1, wherein a ratio of a thickness of the conductive via to a thickness of the conductive pillar is from about 0.33 to 0.55.
 9. The method of claim 1, wherein a ratio of a first width of the conductive via to a second width of the conductive pillar is from about 0.15 to 0.55.
 10. A method of fabricating a semiconductor device, the method comprising: forming a first conductive layer over a contact pad, wherein the contact pad is on a substrate; plating a conductive via on the first conductive layer; forming a passivation layer over the contact pad, wherein a top surface of the conductive via is exposed by the passivation layer; forming a second conductive layer over the conductive via and the passivation layer, wherein the second conductive layer is electrically connected to the conductive via; and plating a conductive pillar over the second conductive layer, wherein a width of the conductive pillar is greater than a width of the conductive via.
 11. The method of claim 10, wherein plating the conductive via comprises: forming a photo-sensitive layer over the first conductive layer; patterning the photo-sensitive layer to form an opening; and plating the conductive via in the opening.
 12. The method of claim 11, wherein patterning the photo-sensitive layer comprises forming the opening having tapered sidewalls.
 13. The method of claim 11, wherein patterning the photo-sensitive layer comprises forming the opening having sidewalls substantially perpendicular to a top surface of the substrate.
 14. The method of claim 10, wherein plating the conductive pillar comprises: forming a photo-sensitive layer over the second conductive layer; patterning the photo-sensitive layer to form an opening; and plating the conductive pillar in the opening.
 15. The method of claim 14, further comprising removing the photo-sensitive layer after plating the conductive pillar.
 16. The method of claim 10, further comprising etching the first conductive layer using the conductive via as a mask.
 17. The method of claim 10, further comprising etching the second conductive layer using the conductive pillar as a mask.
 18. A method of fabricating a semiconductor device, the method comprising: forming a first conductive layer over a contact pad, wherein the contact pad is on a substrate; plating a conductive via on the first conductive layer; etching the first conductive layer to remove portions of the first conductive layer exposed by the conductive via; forming a second conductive layer over the conductive via, wherein the second conductive layer is electrically connected to the conductive via; plating a conductive pillar over the second conductive layer, wherein a width of the conductive pillar is greater than a width of the conductive via; and etching the second conductive layer to remove portions of the second conductive layer exposed by the conductive pillar.
 19. The method of claim 18, wherein plating the conductive via comprises: forming a photo-sensitive layer over the first conductive layer; patterning the photo-sensitive layer to form an opening; and plating the conductive via in the opening.
 20. The method of claim 18, wherein plating the conductive pillar comprises: forming a photo-sensitive layer over the second conductive layer; patterning the photo-sensitive layer to form an opening; and plating the conductive pillar in the opening. 